Hoary Cress or Whitetop
(Cardaria draba)

County Management Strategy: Suppression throughout the County.

Identification: A perennial mustard with an extensive root system and growing up to 2 feet tall. Plants form a dense, contiguous patch. Leaves are slightly toothed, with upper leaves clasping the stem. Numerous small white flowers form a flat-topped flowerhead. Seed pods are heart shaped and contain 2 seeds each.

Other names: Globe-podded hoary cress, globe-podded whitetop, perennial peppergrass

Similar Species: There are many white flowered mustards in our area, however none of them have a dense, flat topped flowerhead. Lens-podded hoary cress (C. chalpensis) and globe podded hoary cress (C. pubescens) occurs in our area and is difficult to distinguish from whitetop; they are treated the same. Perennial pepperweed, or tall whitetop, is much taller, the flowerheads are less dense than hoary cress, and it blooms in mid to late summer.

Control Timing: Before or at very early bloom.

Control Target: Prevent seed production and stress root systems.

Control Methods: Herbicide applications can be very effective on hoary cress when applied at the proper time. Tillage or hand grubbing break up root pieces, which can sprout into new plants. No biocontrol agents are available.

Status in Mesa County: Widespread in lower elevations in the Grand Valley but spreading to higher areas such as Collbran. Common on roadsides. Hoary cress and Russian knapweed are the County’s two most abundant noxious weeds.

Toxicity: DO NOT HANDLE hoary cress with bare hands as it has been known to cause a rash and sensitivity to the sun.

Photos:
http://www.agf.gov.bc.ca/cropprot/weedguid/hoarycr.htm

Fact sheets and control:
http://www.coopext.colostate.edu/TRA/whtop.html
http://www.wildflowers-and-weeds.com/weedsinfo/Cardaria_spp.htm

Additional Links:
http://plants.usda.gov/cgi_bin/topics.cgi?earl=plant_profile.cgi&symbol=LEVU